Abu Laith al-Libi in April 2007 during a videotaped interview by al Qaeda's media wing.

Al-Libi was described as a senior al Qaeda leader believed to have plotted and executed attacks against U.S. and coalition forces, including a February 2007 bombing at Bagram Air Base in Afghanistan during a visit by Vice President Dick Cheney.

He was on a "most wanted" list of 12 accused terrorists which was issued in October by the Combined Joint Task Force-82 -- an anti-terror unit in Afghanistan.

Earlier, a knowledgeable Western official and a military source confirmed al-Libi's death to CNN. The same official said al-Libi is "not far below the importance of the top two al Qaeda leaders" -- Osama bin Laden and Ayman al-Zawahiri.

The officials said al-Libi was killed by a missile from an airplane.

Radical Islamist Web sites announced al-Libi's death.

"May God have mercy on Sheikh Abu Laith al-Libi and accept him with his brothers, with the martyrs," said a eulogy posted on a main Islamist site, Al-Ekhlaas.

Al-Libi, 41, was of Libyan descent and was believed to have been in the Afghanistan/Pakistan border region, according to the U.S. military.

In an earlier role, he was a leader of the Libyan Islamic Fighting Group, which eventually merged with al Qaeda, the counterterrorism official said, and was responsible for planning attacks throughout North Africa and the Middle East. The official described al-Libi as part of al Qaeda's inner circle, who helped fill the void created by the capture or death of other senior people in the organization.

A U.S. military official with Combined Joint Task Force-82 said they have no information on al-Libi's death. But he added that CJTF-82 does not collect information from outside of Afghanistan, and would be informed of targeted operations only "if the Pakistani military share(s) that with us."

The Pakistani military said an explosion occurred in North Waziristan on Tuesday, and 12 people were killed. However, it was unclear whether this was the incident in which al-Libi was killed. Military spokesman Maj. Gen. Athar Abbas told CNN it was not clear who attacked whom and that he could not comment on the identities of the dead since local al Qaeda and Taliban affiliates removed the bodies and buried them.

The U.S. military placed al-Libi on its most wanted list in 2006, behind bin Laden, al-Zawahiri and Taliban leader Mullah Omar. In October, they announced rewards ranging from $20,000 to $200,000 for al-Libi and 11 other mid-level Taliban and al Qaeda leaders.

At that time, the military distributed posters and billboards with pictures and names of the insurgents around eastern Afghanistan.

Al-Libi and the others were described at the time by CJTF-82 spokesman Maj. Chris Belcher as "mid-level bad guys."

He appeared in a 2002 audio recording posted on an Islamist Web site, saying al Qaeda had regrouped and intended to expand its war to include assassinations and attacks against infrastructure.

He also appeared in a 2004 video that showed him participating in an attack on an Afghan army base.

Rep. Peter Hoekstra of Michigan, the top Republican on the House Permanent Select Committee on Intelligence, issued a statement saying al-Libi's reported death would be "a positive development" in efforts against terrorism.

"Intelligence points to, and his [al-Libi's] increasing role in al Qaeda propaganda suggests, that he would have been a top field commander and planner for al Qaeda," Hoekstra said. "His death, if confirmed, clearly will have an impact on the radical jihadist movement."

He said that through the committee, he would monitor the effects on al Qaeda operations. E-mail to a friend